A person's ability
to make crucial driving decisions, such as braking,
steering, or changing lanes is affected by alcohol.
Alcohol slows the rate
of information processing by the brain. This effect
has been noted on many different kinds of tasks even
at the lowest levels of alcohol consumption. For example,
a moderate alcohol dose (0.52 g alcohol/kg body weight)
slowed subjects whose only task was to respond with
the names of familiar, visually displayed objects.
If there are two or more stimuli and if several responses
are possible, response times lengthen significantly.
More complex tasks are even more severely degraded by
Alcohol-impaired drivers require more time to read a
street sign or to recognize and respond to a traffic
signal than those who are not impaired. Consequently,
they look at fewer sources of information and acquire
less total information per unit of time. Because they
must cope with the ongoing requirement to steer the
vehicle, they restrict their looks to the center of
the driving environment, and they may fail to see critical
events occurring elsewhere.